The spirit of the Mediator showed how it was through no punishment of sin that He came to the death of the flesh, because He did not leave it against His will, but because He willed, when He willed, as He willed. For because He is so commingled [with the flesh] by the Word of God as to be one, He says: "I have power to lay down my life, and I have power to take it again. No man taketh it from me, but I lay down my life that I might take it again." And, as the Gospel tells us, they who were present were most astonished at this, that after that [last] word, in which He set forth the figure of our sin, He immediately gave up His spirit. For they who are hung on the cross are commonly tortured by a prolonged death. Whence it was that the legs of the thieves were broken, in order that they might die directly, and be taken down from the cross before the Sabbath. And that He was found to be dead already, caused wonder. And it was this also, at which, as we read, Pilate marvelled, when the body of the Lord was asked of him for burial.
Source: ON THE TRINITY 4.13.16